Peculiar activity of H-Na-mordenite in the N2O abatement with CH4: in situ and operando FTIR study

The catalytic reduction of N 2 O with CH 4 in the absence (CR N2O ) and in the presence of excess O 2 (SCR N2O ) were studied on H-NaMOR catalysts (H-exchange degree within the range 0–100 %) prepared from Na-MOR (Si/Al = 9.2) by ion-exchange method. The catalytic measurements were performed in a flow apparatus with GC analysis of reactants and products. In situ FTIR characterization and catalytic results combined with operando FTIR experiments gave an insight into the active sites for N 2 O abatement and into the reaction pathway. H-NaMOR catalysts were active for both CR N2O and SCR N2O , but inactive for N 2 O decomposition and CH 4 combustion. The activity shows a complex dependence on the H-exchange degree. The active sites involved in the N 2 O reduction are very likely generated by dehydration of pairs of protonated acid sites. Active sites having a specific location are related to the catalytic activity, specifically those located in E sites to CR N2O and those in D sites to SCR N2O . For both CR N2O and SCR N2O the protonation of A sites lowers the activity. The catalytic results combined with operando FTIR characterization suggest that CH 4 and N 2 O cannot be activated separately, but a synergetic activation of N 2 O and CH 4 molecules occurs on a bifunctional active site. Operando FTIR indicated formaldehyde-like species as possible reaction intermediates, as well as the formation of other CH x O y species which poison the catalyst in CR N2O conditions but are easily oxidized in the presence of O 2 during the SCR N2O . • H-NaMOR catalysts are active for N 2 O reduction with CH 4 also in the presence of O 2 . • The active sites are not equivalent depending on their location in the MOR structure. • The active sites for N 2 O reduction are generated by dehydration of Si–OH–Al pairs. • A bifunctional active site coordinates and activates N 2 O and CH 4 at the same time. • Operando FTIR identified formaldehyde-like species as intermediates in N 2 O reduction.